1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head that includes a waveguide, a plasmon generator, and a magnetic pole.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the magnetic recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the aforementioned problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a magnetic recording medium having high coercivity. When writing data, a write magnetic field and heat are applied almost simultaneously to the area of the magnetic recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. As disclosed in, for example, U.S. Patent Application Publication Nos. 2008/0198496 A1 and 2009/0073597 A1, a known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with light. The light for use in generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
A thermally-assisted magnetic recording head that employs a plasmon generator as a source of generation of near-field light is configured so that the write head section includes the plasmon generator and a magnetic pole that produces a write magnetic field. The plasmon generator and the magnetic pole are located in close proximity to each other. In the thermally-assisted magnetic recording head of such a configuration, the plasmon generator and the magnetic pole constitute a main portion of the write head section. Now, a description will be made as to the problems with the thermally-assisted magnetic recording head having the above-described configuration.
Part of the energy of the light guided to the plasmon generator through the waveguide is transformed into heat in the plasmon generator. The plasmon generator and its vicinity therefore increase in temperature during the operation of the thermally-assisted magnetic recording head. The increase in temperature causes the plasmon generator and its vicinity to expand, so that part of the medium facing surface corresponding to the main portion of the write head section protrudes toward the magnetic recording medium.
Typically, the medium facing surface of the slider is covered with and protected by a protective film. Thus, a conventional magnetic head that performs no thermally-assisted magnetic recording will not be seriously damaged even if it comes into contact with the surface of the magnetic recording medium or a dust particle to a certain extent during operation. In the case of a thermally-assisted magnetic recording head, however, the plasmon generator and its vicinity increase in temperature during operation as described above, and this causes part of the protective film, particularly near the plasmon generator, to increase in temperature and become liable to be damaged. The part of the protective film protrudes toward the magnetic recording medium. The part of the protective film is therefore susceptible to damage when brought into contact with the surface of the magnetic recording medium or a dust particle. A serious damage to the part of the protective film would possibly cause the main portion of the write head section (the plasmon generator and the magnetic pole) to be exposed. The main portion of the write head section thus exposed may be damaged. More specifically, the main portion of the write head section may be mechanically damaged when brought into contact with the surface of the magnetic recording medium or a dust particle, or corroded when exposed to a high-temperature moist atmosphere.
U.S. Patent Application Publication No. 2009/0073597 A1 discloses a technology of providing a heat radiating film in the vicinity of a heating mechanism that includes a waveguide and a plasmon generator, in order to reduce the protrusion of part of the medium facing surface caused by the heating mechanism. Even with this technology, however, it is not possible to prevent a temperature increase and the protrusion of part of the medium facing surface caused by the heating mechanism, and consequently it is not possible to avoid damage to the main portion of the write head section.
JP-A-08-287444 discloses a technology of providing a projected portion of a certain height around an MR element on the medium facing surface of the slider to thereby prevent the MR element from coming into direct contact with a magnetic disk.
A thermally-assisted magnetic recording head may also conceivably be configured so that a projected portion of a certain height is provided around the main portion of the write head section on the medium facing surface of the slider in order to prevent the main portion of the write head section from coming into direct contact with the surface of the magnetic recording medium. In the case of the thermally-assisted magnetic recording head, however, the plasmon generator and its vicinity increase in temperature to cause part of the medium facing surface corresponding to the main portion of the write head section to protrude toward the magnetic recording medium, as described above. Furthermore, the amount of protrusion of the part of the medium facing surface varies depending on the ambient temperature. Thus, even if a projected portion of a certain height is provided around the main portion of the write head section on the medium facing surface of the slider, the part of the medium facing surface corresponding to the main portion of the write head section will protrude to come into direct contact with the surface of the magnetic recording medium, thereby possibly causing the main portion of the write head section to be damaged. The height of the projected portion can be increased in order to ensure that the part of the medium facing surface is prevented from directly contacting the surface of the magnetic recording medium. However, this may cause the distance between the main portion of the write head section and the magnetic recording medium to be excessively large, thereby making it impossible to improve the recording density.